Sturgeons

fish rivers species eggs

Sturgeons are large shark-like fish, with a heterocercal tail like that of a shark and a small ventral mouth behind an extended snout. The mouth has long barbells used for feeding on small animals on the bottom. Sturgeons feed on aquatic insects, snails, crayfish, small clams, and small fish.

Sturgeons have a cartilaginous skeleton with bony plates instead of scales in their skin which cover the sides of the body, and which completely cover the head.

Sturgeons are distributed throughout North America, Asia and northern Europe. A few species are anadromous, living in the oceans but swimming up rivers to spawn, and other species live only in fresh water. Of the anadromous sturgeons, one of the two species on the Pacific coast, Acipenser transmontanus, may weigh over 1,000 lb (450 kg). The two anadromous species on the Atlantic coast have been recently greatly reduced in population.

Sturgeons are found both in the rivers and the eastern coasts of North America. The most common species in North America is the lake sturgeon, Acipenser fulvescens. In Europe they are found in the rivers and the coast line from Scandinavia to the Black Sea. From time to time trawlers fishing along the coasts of Britain and Ireland may catch sturgeons. Pollution and the presence of weirs have been instrumental in reducing the populations to the point of extinction in rivers where they were once plentiful.

Spawning occurs from May to July when the sturgeons enter the rivers of the United States and continental Europe. A female sturgeon may lay up to three million eggs, each about 0.08 in (2 mm) in diameter, and covered with gelatin. Eggs remain on the bottom of the river, hatch within 3–7 days, and release larvae that measure about 0.4 in (9 mm). At one month the young fish may measure 4-5.5 in (10-14 cm) long. The young may not start the seaward journey until they reach two or three years of age and are 3.3 ft (1 m) long.

The flesh of the sturgeon is edible but is not prized; it is the sturgeon's eggs used to make caviar that are in great demand. The swim bladders of sturgeons are used to make isinglass, a semi-transparent whitish gelatin used in jellies, glues, and as a clarifying agent.

Since the population of sturgeons has been greatly diminished, commercial fishing of these fish is now limited. Some sturgeons may provide considerable excitement because of the battle they provide when hooked on light tackle.

The sturgeon family has the distinction of providing the largest freshwater fish in North America. In the last century three fish were reported to exceed 1,500 lb (680 kg). At present some specimens may weigh over 1,000 lb (450 kg), and one fish caught by gill net weighed 1,285 lb (584 kg). Although the species extends from Alaska to
A lake sturgeon (Acipenser fulvescens).Photograph by Tom McHugh. Photo Researchers, Inc. Reproduced by permission.
the middle of California, the largest fish are found mainly in the Columbia and Fraser rivers in British Columbia, Washington, and Oregon.

The white sturgeon is actually grayish brown with a white belly. When at 9 ft (2.7 m) long, it may be about 50 years of age. The 3,000,000 eggs laid by a 10–foot female may weigh almost 250 lb (113 kg). Laws protecting large sturgeons, which tend to be females with eggs, are now in effect.

The green sturgeon, A. medirostris, grows up to 7 ft (2.1 m) and weighs about 350 lb (159 kg). It has a greenish color and its barbells are located nearer to the end of the snout, and has fewer bony plates along the back.

The largest fish caught in fresh water along the Atlantic coast is the Atlantic sturgeon, A. oxyrhynchus. It has been verified that a 14–ft (4.3–m) fish weighing 611 lb (278 kg) has been caught. As is the case with the Pacific sturgeon, the Atlantic sturgeon populations are being depleted because of pollution and dams, which prevent them from reaching their breeding grounds.

Nathan Lavenda

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